Is Sleeping Good for the Heart?

Time to relax around the Christmas dinner table with family and friends.

Time to catch up on sleep?

For those who are always looking for an excuse to sleep in, or sleep more, your search is not in vain: According to new research, hours spent sleeping protects against calcium deposits in the coronary arteries -- the deposits responsible for heart attacks.

A study published this week in the Journal of the American Medical Association by Christopher King and colleagues from the University of Chicago has found a relationship between sleep quantity (hours spent asleep) and calcium build up -- or calcification -- in the arteries that supply the heart muscle with blood.

For each additional hour of sleep, the risk of calcification of the coronary arteries decreased by 33 percent -- an outcome equal to reducing blood pressure by 16 point elevations.

Moreover, the sleep relationship did not change even when the researchers controlled for certain traditional risk factors for heart disease, such as cholesterol, weight and diabetes.

The results were part of the ongoing Coronary Artery Risk Development in Young Adults Study (CARDIA), which is being carried out at four cities nationally.

This report focused on nearly 500 patients at the Chicago CARDIA site.

Participants were black and white men and women aged 35-47 years, measured initially in 2000-2001 and followed up in 2005-2006.

Sleep was measured by a wrist band recording wrist movement on an initial Wednesday through Saturday night period.

This wrist recorder is a very good measurement of time spent asleep -- nearly as good as sleep measured in a sophisticated sleep laboratory.

However, the wrist band is less disruptive to normal sleep than sleeping in a sleep lab, because there is no "first-night" effect -- the disruption of the normal sleep structure of a subject that is often seen with more intrusive testing.

The amount of calcium in the coronary arteries was measured by CT scanning of the heart.

Linking Zzz's and Heart Disease

The authors do not know why sleep seems to be associated with less calcification; however, they propose three possible explanations.

First, there may be unknown factors common to both sleep and heart disease -- factors the researchers did not know to measure.

Second, inflammation elsewhere in the body increases the risk of calcification, and this effect can be influenced by the body's natural anti-inflammatory hormone, cortisol. This hormone is released in sync with a person's sleep patterns. Increased time asleep might increase the release of cortisol -- which, in turn, might reduce inflammation and, therefore, calcium deposits.

Third, blood pressure declines during sleep. Thus, it might be the case that the longer people sleep, the less their heart is exposed to elevated blood pressure.

The authors note that this is the first study to find a relationship between sleep and coronary artery calcium deposits. Other studies have looked at sleep apnea -- periods during sleep when an individual stops breathing.

Sleep apnea is associated with high blood pressure and heart attacks, but the authors did not measure this sleep phenomenon.

The authors conclude that "this study demonstrates that objectively measured sleep is inversely associated with coronary artery calcification. This study further demonstrates the utility of a simple objective measure of sleep that can be used at home. Future studies will be needed for crucial extensions to these results."

So, happy holidays.

And get some sleep!

Dr. John Spangler is director of tobacco intervention programs and a professor of family medicine at Wake Forest University School of Medicine in North Carolina.